My advice is to try them out yourself (live CD versions if possible) and then give us your view.

I use SUSE 9.2 but only because it is the most compatible that I have found with this system. I have no reason to prefer suse over other distros (and i have tried lots of them) except that suse 9.2 is the most compatible for me to date.

Using applications appears the same whatever distro is in the background. KDE is KDE on any distro, the version changes of KDE are usually more "different" than say KDE 3.2 on mandrake and KDE 3.2 on suse.

lol (from a linux noob)thats exactly what i did. bought a 120 gig hd to keep it all apart from windows and started installing distros (7 or 8 so far).the equipment has a lot to do with it from what i was told, and some are easier to install. i have dual xeons, scsi and quadro pro. fedora 3 smp kernel was very unstable, wont mount ntfs, and needs work to do the soundcard and video correctly

mandrake 10.1 smp is very very stable. mounts ntfs, detects the soundcard out of the box and was the easiest to install (also the fastest, about 20 min)

debian only compiled a single proc kernel. and i really mean a single (it worked against the hyperthreading) it mounts ntfs but was a pain to get the soundcard working right

gentoo has a great community for information, nicely keeps up with the newest source code and is working great with the hardware but u have a lot of work to install it.